The gene regulation relating to malignancy that was studied included novel primate retrovirus expression, chromosomal integration sites of pp-1 (Papio papio) and Rous sarcoma virus in human tumor cells, and modulation of human chorionic gonadotropin, alkaline phosphatase, type IV collagen, and collagenase. The effort to induce new primate retroviral expression centers around three areas: (1) use of cell fusion and chromosome segregation; (2) transfection by the early region of SV40 DNA of unusual cell strains to obtain permanent indicator lines to overcome host range restriction; and (3) use of Rhesus monkey and human placental tissue as target cells for retroviral isolation. Somatic cell hybrids between infected human and rodent cells, preferentially losing human chromosomes, are being used to determine which human chromosome(s) integrate the proviral DNA's of PP-1 and RSV. Optimal methods have been developed for growth of human placenta in organ culture and for isolation of trophoblast cells for growth in monolayer culture. The mechanism of modulation of HCG, PAP, type IV collagen and collagenase with cyclic nucleotides and metabolic inhibitors is being compared in human choriocarcinoma and normal human trophoblast tissue.